Apertured conditioning brush for chemical mechanical planarization systems

ABSTRACT

An apparatus for conditioning the polishing pad of a chemical mechanical planarization (CMP) system including an apertured conditioning disk that is formed to support a plurality of brush bristles in any desired configuration. The bristles are utilized to lift out debris and contaminants that have been lodged within the deep pores of polishing pads, particularly “soft” polishing pads (or polishing felts) that include relatively deep pores. The apertures in the conditioning disk are used to allow for the efficient evacuation of the effluent created during the conditioning process. The apertures may also be used to introduce conditioning fluids as the bristles are brushing the surface to assist in the conditioning process. The utilization of the apertures to evacuate the effluent (via an attached vacuum source) overcomes problems associated with the prior art by immediately removing the dislodged material from the pad surface before it has an opportunity to be re-incorporated into the polishing pad.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/728,126, filed Oct. 19, 2005 and herein incorporated by reference.

TECHNICAL FIELD

The present invention relates to a conditioning brush for use incleaning the polishing pad of a chemical mechanical planarization (CMP)apparatus and, more particularly, to a conditioning brush formed as diskto include an arrangement of both bristles and apertures to facilitatethe cleaning operation.

BACKGROUND OF THE INVENTION

In the field of chemical mechanical planarization (CMP), a process knownas “pad conditioning” or “pad dressing” is used to restore the surfaceof the polishing pad and remove surface glazing by dislodgingparticulates and spent polishing slurry from the pad. Pad conditioningmay be performed “ex-situ” (i.e., conditioning the polishing pad betweenwafer polishing cycles) or “in-situ” (i.e., concurrent with, or during,a wafer polishing cycle). In a typical prior art “in-situ” padconditioning process, a fixed abrasive conditioning disk is moved acrossthe pad surface to remove a small amount of pad material and debris,thus creating new asperities in the pad surface to allow for the freeflow of the polishing slurry. The removed pad material and debris thencombine with the slurry dispensed during the polishing process and arepassively carried away from the pad.

Particulate generation is an on-going problem with known processes ofconditioning CMP polishing pads, where particles from any one of the CMPapparatus, slurry, wafer, pad or conditioner remain on the pad's surfaceafter conditioning. Any individual particle remaining on the pad maylater scratch a wafer surface during polishing, creating a potentialdefect or contributing to polishing non-uniformity. For example, aparticle disposed on the polishing pad may create a high spot thatlocally concentrates the forces between the polishing pad and the wafer.If large numbers of particles are present on the polishing pad, localdisparities in polishing rates may result in polishing non-uniformities.

In certain types of CMP, for example tungsten CMP or post-planarizationbuffing, a relatively porous polishing pad is utilized, where this typeof pad is characterized by a microstructure exhibiting verticallyoriented, open pores. Variously referred to as a “soft” polishing pad,fibrous polishing pad, and the like, such pads may consist of aporomeric coating over a felt substrate, the poromeric coatingcomprising vertically oriented large pores sitting on top of a smaller,microporous felt layer. The polishing slurry and debris that settleswithin the lower regions of the pores within these pads can becomenearly stagnant and develop recirculating eddy flows that trap even morematerial and limit the polishing/buffing capabilities of the pad. Overtime, the trapped/recirculated materials can resurface and damage thewafer, dilute the process materials, or both. The conventional diamondabrasive conditioning disk is not effective in removing thisdeeply-trapped material, and has the additional drawback of quicklywearing away the porous pad material. As an alternative, a conditioning“brush” may be used to scour the porous pad surface in a manner that islikely to dislodge deeply embedded particles and move them into thewaste stream. Prior art CMP systems utilizing a conditioning brush,however, require a large amount of slurry and rinse waters in an attemptto displace these particulates.

U.S. Pat. NO. 6,386,963 issued to S. Kenji et al. on May 14, 2002discloses a conditioning element that is formed to support a combinationof an abrasive surface and brush bristles. In the Kenji et al.structure, abrasive conditioning material is formed on a ring-shapedplate that is attached to the bottom surface of the conditioner head,leaving the center region of the element open. A plurality of brushbristles is formed on a small disk that is then attached to the centerregion of the abrasive ring. One problem with this particulararrangement, however, is that the limited positioning of the bristles inthe central region of the conditioning element allows some particulatematter to be unaffected by the bristles and thus remain embedded withinthe pad. Further, the differential in height between the abrasivematerial and the bristles will likely result in inconsistentconditioning behavior and wear rates for the pad material.

Another prior art arrangement is disclosed in U.S. Pat. No. 7,033,253,issued to F. L. Dunn on Apr. 25, 2006. In the Dunn arrangement, brushbristles are disposed in any desired pattern on the bottom surface of aconditioning element, with the remaining portion of the surface coveredby an abrasive material. The relative hardness of the bristles and theabrasive material may be controlled to best condition a particular padmaterial.

While both the Dunn and Kenji et al. arrangements provide an improvementin implementing a conditioning brush within a conventional CMPconditioning element, problems remain in that the material dislodged bythe bristles (and the abrasive material) may be re-introduced to the padsurface before the conditioning process has an opportunity to flush thedebris away.

Thus, a need remains in the art for a conditioning arrangement thatprovides the brushing motion preferred for large pore, fibrous or softpolishing pads/felts, while efficiently removing the debris from thepolishing pad surface.

SUMMARY OF THE INVENTION

The need remaining in the prior art is addressed by the presentinvention, which relates to a conditioning brush for use in cleaning thepolishing pad of a chemical mechanical planarization (CMP) apparatusand, more particularly, to a conditioning brush formed as a disk toinclude an arrangement of both bristles and apertures to facilitate thecleaning operation.

In accordance with the present invention, an apertured conditioning diskis formed to support a plurality of brush bristles in any desiredconfiguration. The apertures in the conditioning disk are used to allowfor the efficient evacuation of the effluent created during theconditioning process, including both the debris dislodged by thebristles and slurry material remaining in the pores. The apertures mayalso be used to introduce conditioning fluids to assist in theconditioning process. The utilization of the apertures to evacuate theeffluent (via an attached vacuum source) overcomes problems associatedwith the prior art by immediately removing the dislodged and/oraccumulated material from the pad surface before it has an opportunityto be re-incorporated into the polishing pad.

In one embodiment of the present invention, the conditioning disk isformed of a stiff material capable of supporting the bristles inposition such that the bristles have a slight stand-off from the bottomsurface of the disk, allowing for the conditioner head to maintain avacuum seal while the bristles engage the pores of the pad material. Inan alternative embodiment, the conditioning disk may be formed of anabrasive material to permit simultaneous abrading and brushing of thepolishing pad surface. In yet another embodiment, the bristlesthemselves may be formed of an abrasive-filled composite material.

Other and further embodiments and aspects of the present invention willbecome apparent during the course of the following discussion and byreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings,

FIG. 1 illustrates an exemplary CMP system including a conditioningbrush formed in accordance with the present invention;

FIG. 2 is a top view of system of FIG. 1;

FIG. 3 is a top view of an exemplary conditioner head/conditioning brushformed in accordance with the present invention, include a plurality ofbristles and a separate plurality of apertures within the brush;

FIG. 4 is a cut-away side view of the conditioning brush of FIG. 3;

FIG. 5 is a simplified view of the arrangement of FIG. 4, illustratingin particular the intrusion of the bristles within the pores of thepolishing pad;

FIG. 6 is a top view of an alternative embodiment of the presentinvention, with the bristles disposed in V patterns and the aperturesdisposed therebetween, the view of FIG. 6 illustrating the placement ofonly a few bristles;

FIG. 7 is a top view of the same embodiment as FIG. 6, in this case witha complete set of bristles in place; and

FIG. 8 is a top view of yet another embodiment of a conditioning brushformed in accordance with the present invention, in this case, thebristles and apertures disposed as a plurality of arms configured in aspiral pattern from the center.

DETAILED DESCRIPTION

FIG. 1 contains a perspective view of an exemplary CMP system 10 formedin accordance with the present invention for brushing the surface of apolishing pad used to polish/planarize surface S of a semiconductorwafer 12. In operation, surface S of wafer 12 is positioned against apolishing pad 14 through an arrangement not shown (and not relevant tothe subject matter of the present invention). Wafer 12 is rotated onpolishing pad 14, as shown by the arrow in FIG. 1. Polishing pad 14itself is secured to a rotating, orbital or linear platen 16. A streamof polishing slurry, generally containing an oxidizer, abrasive and/orultrapure water (UPW) is poured on polishing pad surface 18 from aconventional polishing slurry delivery apparatus (not shown). Thepolishing slurry, in cooperation with the rotating motion of wafer 12and pad 14, acts to remove a portion of the wafer's surface unevenness.

As mentioned above, it is necessary to “condition” or “redress” surface18 of polishing pad 14 to remove the glaze/build-up of polishing slurryfrom the pad's surface, as well as to remove accumulated debris andother materials associated with the polishing process itself. In thearrangement as shown in FIG. 1, an end effector arm 20 is used toperform the conditioning process, where arm 20 moves in an arc A about afixed shaft 21 and simultaneously provides a rotational motion R and adownward force F on an attached conditioner head 22. FIG. 2 shows, in atop view, the relative motions of arm 20, conditioner head 22 andpolishing pad 14, illustrating in particular arc movement A of arm 20across the surface of polishing pad 14. In an alternative embodiment,the end effector can be configured to cover a full radius of polishingpad 14, such that it conditions surface 18 without the need of thearc-based sweeping motion. The apertured conditioning brush of thepresent invention, as discussed in detail below, may be used with eitherembodiment. The apertured conditioning brush of the present invention isequally applicable for use in systems that include polishing feltsinstead of polishing pads, where the felts have the same deep napconfiguration as the soft polishing pads discussed above. That is, thepolishing pads and polishing felts best suited for conditioning with theapertured brush of the present invention are characterized by amicrostructure exhibiting vertically oriented, open pores (e.g.,poromeric coating), capable of trapping debris and fluids inrecirculating eddies, as discussed above.

Referring back to FIG. 1, conditioner head 22 is shown as furthercomprising an apertured conditioning brush 30, formed in accordance withthe present invention to perform the functions of: (1) brushing surface18 of polishing pad 14 to loosen debris lodged deep within pad 14; (2)evacuating the conditioning fluid, dislodged debris and/or spentpolishing fluid (hereinafter referred to as “effluent”) from thevicinity of polishing pad 14; and, possibly, (3) introducingconditioning fluids onto surface 18 of pad 14. Conventional abrasiveconditioning disks are not always successful in removing debris deeplyembedded within the pores of some of the more fibrous polishing pads andpolishing felts. A plurality of bristles, as described below, areincluded in contacting surface 31 of conditioning brush 30 and willenter the deep pores of the fibrous polishing pad to dislodgeaccumulated debris. Apertures formed within conditioning brush 30provide a channel for the removal of effluent through a vacuum path,where in FIG. 1 conditioner head 22 is illustrated as including a vacuumoutlet port 37 coupled to a vacuum source 50. Conditioning fluids may beused in combination with the surface brush to efficiently removeaccumulated debris, where the conditioning fluids may be disposed ontothe surface of polishing pad 18 through an inlet port 39 in conditionerhead 22.

FIG. 3 contains a top view of an exemplary apertured conditioning brush30 as fixed within conditioner head 22, where illustrated surface 31will contact the surface of a polishing pad during conditioning. Thereexist various arrangements for attaching conditioning brush 30 toconditioner head 22, where a particularly suitable arrangement thatmaintains apertured alignment between brush 30 and the remainingcomponents of conditioning disk 22, using a magnetic-based hex keyarrangement, is disclosed in co-pending application Ser. No. 10/819,754,filed Apr. 7, 2004, and assigned to the assignee of this application.Referring to FIG. 3, a plurality of apertures 34 are shown, whereapertures 34 are surrounded by a plurality of bristles 40 that functionto provide the soft pad brushing in accordance with the presentinvention. FIG. 4 is a cut-away side view of the arrangement of FIG. 3.Bristles 40 function to dislodge particulate matter from the fibrouspores below surface 18 of pad 14 (see FIG. 5) and push the effluentthrough apertures 34 toward vacuum outlets 35 around the outer peripheryof conditioner head 22, as shown in FIG. 4. The rotation of conditionerhead 22 will assist in moving the effluent outward through vacuumoutlets 35 into an evacuation channel 36. The effluent is then pulled,by vacuum force, through vacuum exit port 37 on conditioner head 22,providing an efficient cleaning of polishing pad surface 18. In theparticular embodiment as illustrated in FIG. 4, conditioning brush 30further comprises a channel system 32 coupled to apertures 34 to allowfor the introduction of conditioning fluids, if desired, via inlet port39 of conditioner head 22.

FIG. 5 illustrates, in a simplified view, the relationship between pad14, conditioner head 22 and bristles 40. As mentioned above, bristles 40are formed to stand off a predetermined distance below conditioner head22, allowing for bristles 40 to enter the deep, soft-walled pores ofpolishing pad 14 during conditioning, while maintaining the integrity ofthe vacuum connection or seal between pad 14 and conditioner head 22. Asshown, bristles 40 extend deep enough into vertically-oriented openpores P of pad 14 so that the accumulated debris may be dislodged asconditioning brush 30 sweeps across the pad surface. The length ofbristles 40 is controlled, however, so that sidewalls 22W of conditionerhead 22 maintain contact with surface 18 of polishing pad 14. It is tobe understood that the particular dimensions of the bristles will be afunction of parameters such as, but not limited to, the depth of thepores of the fibrous polishing material, the pad material itself, thedownforce applied by the conditioner head to the polishing pad, and theapplied vacuum force. The contact between surface 18 and conditionerhead sidewalls 22W is required so that the vacuum force/leakage iscontrollable and the debris will continue to be evacuated from padsurface 18, through conditioning brush 30 and exit from vacuum outletport 37 of conditioner head 22. Bristles 40 comprise an inert material,such as nylon, that will not react with any of the chemicals that may bepresent at the pad surface, such as polishing slurry, conditioningliquids, wafer debris material and the like. In a specific embodiment,bristles 40 may be formed of an abrasive-filled composite material thatwill provide an even greater amount of cleaning energy to surface 18 ofconditioning pad 14.

FIG. 6 is a top view of an alternative conditioning brush 60, where inthis particular embodiment, bristles 40 are disposed in V-like patterns62 across surface 61 of brush 60. For the sake of clarity, only aportion of bristles 40 are shown in position in FIG. 6. FIG. 7 is a topview of conditioning brush 60 with a complete set of bristles 40 inplace. Referring back to FIG. 6, a set of apertures 34, is shown asdisposed between each V pattern 62 of bristles. Apertures 34 function inthe manner discussed above to dispense conditioning liquids and evacuateeffluent from surface 18 of polishing pad 14.

FIG. 8 contains a top view of yet another embodiment of an aperturedconditioning brush formed in accordance with the present invention. Inthis arrangement, a conditioning brush 70 comprises bristles 40 arrangedin a set of spiral arms 72 emanating from a central area 74 of brush 70.Apertures 34 are similarly arranged in a spiral arm configuration, witha separate set of apertures 34 disposed between adjacent sets ofbristles 40. As with the arrangement described above in association withFIG. 4, bristles 40 and apertures 34 of brush 70 are designed so as tochannel the debris toward the outer periphery for efficient removalthrough evacuation.

It is to be understood that the apertured conditioning brush of thepresent invention can be used in association with any type of polishingpad, or polishing felt, but is preferably intended for use with thefibrous polishing and/or buffing pads as discussed above that consist ofdeep, soft-walled, vertically-oriented pores conducive to the creationof recirculating eddy currents deep within the pad that trap the debrisand spent slurry. The apertured conditioning brush of the presentinvention may also be utilized with conventional (i.e., relatively“hard”) polishing pads, where abrasive bristles provide sufficientsurface abrasion, with lower pad wear rates, than traditional abrasiveconditioning disks. Moreover, the arrangement of the bristles andapertures across the surface of the conditioning brush may be modified,as need be, to suit the needs of the particular CMP system. Indeed, thesubject matter of the present invention is intended to be limited onlyby the scope of the claims appended hereto.

1. An apparatus for conditioning a polishing pad utilized in a chemical mechanical planarization (CMP) system, the apparatus comprising a conditioner head housing including an inlet port for introducing conditioning fluids onto the polishing pad and an outlet port for evacuating conditioning effluent from a conditioned area of said polishing pad; and a conditioning disk disposed within the housing so as to contact a top major surface of the polishing pad surface during conditioning, the conditioning disk comprising a brush for sweeping the top major surface of the polishing pad and dislodging debris therefrom, and a plurality of apertures for dispensing conditioning fluids to, and evacuating conditioning effluent from, the polishing pad.
 2. An apparatus as defined in claim 1 wherein the brush comprises a plurality of bristles.
 3. An apparatus as defined in claim 1 wherein the conditioning disk comprises an abrasive material.
 4. An apparatus as defined in claim 2 wherein the plurality of bristles comprises an inert material.
 5. An apparatus as defined in claim 4 wherein the inert material comprises nylon.
 6. An apparatus as defined in claim 2 wherein the plurality of bristles comprises a composite abrasive-filled material.
 7. An apparatus as defined in claim 2 wherein the plurality of bristles is disposed in a series of nested V-patterns across the conditioning disk, with the apertures disposed therebetween.
 8. An apparatus as defined in claim 2 wherein the plurality of bristles is disposed in a series of concentric circles across the conditioning disk.
 9. An apparatus as defined in claim 2 wherein the plurality of bristles is disposed in a plurality of spiral arms emanating from a central region of the conditioning disk.
 10. An apparatus as defined in claim 2 wherein the plurality of bristles stand off a predetermined distance below the conditioner head housing so as to allow for the bristles to enter the polishing pad material without interrupting the evacuation of effluent therefrom.
 11. An apparatus as defined in claim 1 wherein the conditioning disk further comprises a hex key alignment structure for providing aligned attachment between the conditioning disk and the conditioner head housing, providing alignment between the plurality of apertures of said conditioning disk and the inlet and outlet ports of said conditioner head housing.
 12. A conditioning disk for use in dressing a polishing pad within a chemical mechanical planarization (CMP) apparatus, the conditioning disk comprising a plurality of apertures for dispensing conditioning fluids to, and evacuating conditioning effluent from, the polishing pad surface; and a brush for sweeping across the fibrous polishing pad and dislodging debris therefrom.
 13. A conditioning disk as defined in claim 12 wherein the brush comprises a plurality of bristles.
 14. A conditioning disk as defined in claim 12 wherein the disk comprises an abrasive material suitable for dressing the polishing pad.
 15. A conditioning disk as defined in claim 13 wherein the plurality of bristles comprises an inert material.
 16. A conditioning disk as defined in claim 15 where the inert material comprises nylon.
 17. A conditioning disk as defined in claim 13 wherein the plurality of bristles comprises a composite abrasive-filled material.
 18. A conditioning disk as defined in claim 13 wherein the plurality of bristles is disposed in a series of nested V-patterns across the conditioning disk, with the plurality of apertures disposed therebetween.
 19. A conditioning disk as defined in claim 13 wherein the plurality of bristles is disposed in a series of concentric circles across the conditioning disk.
 20. A conditioning disk as defined in claim 13 wherein the plurality of bristles is disposed in a plurality of spiral arms emanating from a central region of the conditioning disk.
 21. A method of conditioning a polishing pad utilized in a chemical mechanical planarization system, the method comprising the steps of: presenting an apertured conditioning brush against a top major surface of the polishing pad, the apertured conditioning brush comprising a plurality of bristles and a plurality of apertures; providing a downforce on the apertured conditioning brush sufficient to push the plurality of bristles into the pores of the polishing pad; moving said apertured conditioning brush across the surface of said polishing pad such that the plurality of bristles dislodge accumulated debris from the pores; and applying a vacuum force sufficient to evacuate the dislodged accumulated debris through the plurality of apertures and away from the chemical mechanical planarization system.
 22. The method as defined in claim 21 wherein the method further comprises the step of dispensing processing fluids onto the surface of the polishing pad as the apertured conditioning brush is moved across the surface of the polishing pad.
 23. The method as defined in claim 21 wherein the applied downforce and the vacuum force are controlled so as to allow for the plurality of bristles to engage the pores of the polishing pad without interrupting the vacuum-controlled evacuation of the dislodged debris therefrom. 